The present invention relates generally to an air intake muffler (silencer) for an engine and, more particularly, to an air intake muffler for a vertical multi-cylinder engine for use in an outboard engine assembly.
An air intake muffler (silencer) of this kind is disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI-8-93433. The air intake muffler has an overall box shape which is composed of a flat base plate, a plurality of air horns mounted on the base plate so as to protrude toward the inside of the box, and a case covering the base plate. The base plate and the case are joined to one another in a unitary structure to form the box shape. The air horns form air intake connecting passages which communicate with a throttle of the engine. Since outermost surfaces of the air horns are flat, a difficulty is encountered in connecting a terminal end portion of the air intake passage or path of the throttle valve unit to the air horns and in sealing the joint portions, with a resultant difficulty in ensuring a sealing property in high precision.
Further, since the air horns are so arranged as to protrude in an internal space of the air intake muffler to allow the same to be connected to the air intake passage of the throttle valve unit in an easy and reliable manner, although it is thinkable to provide fitting-type joint portions to the outermost surfaces of the air horns, the base plate of the air intake muffler becomes complicated in structure causing intricate and troublesome manufacturing processes.
Furthermore, although there is a need for locating an outside air intake opening, in addition to the air intake connecting passage, in the air intake muffler and the prior art practice contemplates the provision of apertures in the box-shaped air intake muffler, the use of the apertures encounter a problem in view of an air intake efficiency. As a consequence, it is preferable for a cylindrical member to be incorporated in order to obtain a tube-length effect (wherein induction noise, generated by vibration of air caused during air sucking, is substantially determined by the dimension of the intake pipe), with a resultant increase in the number of component parts causing the need for providing a sealing structure between the cylindrical member and the air intake muffler, resulting in an additional increase in the number of component parts, a complicated structure and an increased cost.
In the outboard engine assembly, further, since the air intake muffler is mounted to one of areas in fore and aft directions of the vertical type engine with a vertical crankshaft, the outboard engine assembly involving the engine is largely sized in structure in fore and aft directions.
It is therefore an object of the present invention to provide an air intake muffler which is unitarily formed with a cylindrical outside air intake opening having a cylindrical joint opening, to be connected to a throttle valve unit, and a tube-length effect without requiring additional component parts in manufacturing stages of a box-shaped muffler body.
According to a first aspect of the present invention, there is provided an air intake muffler for introducing outside air to feed the same to an air intake passage of a throttle valve unit of an engine, which muffler comprises a box body, an air intake connecting duct adapted to be connected to the air intake passage, and at least one outside air intake duct for introducing the outside air into the box body, wherein the box body includes two halves by one of which the air intake connecting duct is unitarily formed so as to protrude outwardly, and the outside air intake duct is formed by mating concave portions to one another which are unitarily formed with both of the two halves so as to protrude outwardly.
The box-shaped air intake muffler body is able to be unitarily formed with the air intake connecting duct, to be connected to the throttle valve unit, and the outside air intake duct without the need for additional component parts except for the upper and lower halves in stages of manufacture of the air intake muffler body by allowing dish-shaped two halves to be mated to and jointed to one another. As a consequence, manufacture can be easily performed without need for additional component parts, with a resultant decrease in the number of component parts while cutting costs.
Further, the body of the air intake muffler is formed into dish-shaped two halves, one of which is unitarily formed with the air intake connecting duct and the other one of which is unitarily formed with the concave portion which forms a remaining half of the outside air intake duct. Accordingly, during manufacture of the air intake muffler, merely jointing the halves to one another by means of adhesion or screw tightening, etc, enables the air intake muffler, having the air intake connecting duct and the outside air intake duct, to be easily manufactured.
Furthermore, since the air intake connecting duct and the outside air intake duct are unitarily formed with the body of the air intake muffler, there is no need for the muffler body, and the air intake connecting duct and the outside air intake duct to be sealed off.
The outside air intake duct of the air intake muffler includes, for example according to examples of the preferred embodiments, two components, with these two outside air intake duct components being formed in a V-shaped configuration so as to diverge rearwardly. Thus, the presence of two outside air intake ducts whereas a single air intake connecting duct to be connected to the throttle valve unit is provided improves air intake efficiency with favorable reduction in induction noises.
The two halves are composed of upper and lower half components, and the air intake connecting duct and the outside air intake duct are located in a horizontal direction. Thus, the presence of the air intake connecting duct and the outside air intake duct extending in the horizontal direction enables the height of the air intake muffler to be limited to a minimum value to allow, for example, the use of the air intake muffler for the outboard engine assembly for thereby making it possible to miniaturize the outboard engine assembly.
One of the two halves of the air intake muffler is formed with a retaining frame at a position wherein the air intake connecting duct is formed to allow a peripheral edge of a flame arrester, which is composed of a mesh member, to be inserted in the retaining frame such that the flame arrester is mounted in the retaining frame. During the course of mating and jointing the two halves to one another, it is possible for the air intake muffler to be easily manufactured under a condition wherein the mesh member, which forms the flame arrester mounted to the retaining frame formed in one of the halves, is internally incorporated. The flame arrester is mounted in the retaining frame in a plane perpendicular to an axis of the air intake connecting duct.
According to a second aspect of the present invention, there is provided an outboard engine assembly which comprises an engine, and an air intake muffler located above the engine and including an air intake connecting duct connected to an air intake passage of a throttle valve unit of the engine, and at least one outside air intake duct for introducing outside air.
In the thus arranged outboard engine assembly, presence of the air intake muffler located above the engine allows an upper surface of the engine to be effectively utilized. According to the preferred embodiments, for example, the engine comprises a V-type multi-cylinder vertical engine wherein the air intake muffler having a substantially flat bottom wall is placed above a drive pulley, driven by a crankshaft of the engine, and a belt engaging the drive pulley. That is, since the air intake muffler is located above the belt, etc. which is positioned above the engine, the belt and the engine are opened at their side areas to provide an improved heat dissipating property of the belt and the engine.